Studies concerning the molecular mechanisms controlling gene expressing in Trypanosoma cruzi were initiated. We attempted, in our approach, to identify T. cruzi genes which might share DNA homology with known transcriptional activators in yeast (e.g., GCN4) and mammalian cells (e.g., c-fos and c-myc). We found that T. cruzi DNA, in dot-blot hybridization experiments, hybridizes under stringent conditions with the c-fos- and GCN4-specific probes, but not with a probe specific for c-myc. Further analysis by Southern hybridization revealed that the c-fos-specific probe hybridizes to a single 8.1 kb band in EcoRI-digested T. cruzi DNA. The cloning and sequencing of this 8.1 kb DNA fragment should allow the identification of any c-fos-related genes contained within it. Moreover, if this putative fos-related gene proves to be developmentally regulated, the DNA sequence data may help to identify regions involved in controlling its expression.